In recent years, with the development of electronics technology, mobile electronic devices such as cellular phones and laptop personal computers, and in-car electronic devices to be installed on cars have becoming common, and the reduction in size with multiple functions has been required for the electronic devices. On the other hand, in order to achieve the reduction in size with multiple functions for the electronic devices, more semiconductor elements have been used such as various types of ICs and LSICs, and accordingly, there have been a need for measures against noises from the electronic devices.
As the measures against noises from the electronic devices, power lines for semiconductor elements are provided with a film capacitor, a laminate-type ceramic capacitor, a semiconductor ceramic capacitor, or the like as a bypass capacitor. In particular, in the case of car navigation systems, car audio systems, in-car ECUs, etc., it is common that a capacitor with an electrostatic capacitance on the order of 1 nF is connected to an external terminal to absorb high-frequency noises.
However, the electrostatic capacitance lowered on the order of 1 nF makes the ESD (Electro-Static Discharge) withstanding voltage extremely low (for example, on the order of 2 kV to 4 kV), thereby possibly leading to breakdown of the capacitor itself. Therefore, as a measure against ESD, it is often the case that a varistor or a zener diode is used in parallel connection to the capacitor.
On the other hand, SrTiO3 based grain boundary insulated semiconductor ceramics are known to have varistor characteristics. The varistor characteristics refer to characteristics of large currents which flow when voltages of not less than a certain value are applied. The use of the varistor characteristics eliminates the need for connections to varistors or zener diodes as in the case of conventional capacitors, and thus can provide capacitors which have the function of an ESD withstanding voltage by themselves.
Therefore, the development of capacitors using these grain boundary insulated semiconductor ceramics has been advanced.
For example, Patent Document 1 discloses a SrTiO3 based grain boundary insulated ceramic powder that has a donor element in crystal grain boundaries as a solid solution, also an acceptor element present at least in the crystal grain boundaries, an integral width of 0.500° or less at the crystal face (222), and an average powder grain size of 1.0 μm or less for the crystal grains. In addition, semiconductor ceramic capacitors prepared with the use of a semiconductor ceramic obtained by firing the ceramic powder are considered to be able to prevent the capacitor itself from being destroyed, even when high voltages are applied.    Patent Document 1: International Publication No. WO 2009/001690